Magnetic recording medium and recording/reproducing method therefor as well as information processing apparatus by means thereof

ABSTRACT

The present invention relates to a magnetic recording medium of a disk shape having a magnetic layer containing a magnetic material formed on a non-magnetic support and having, between the non-magnetic support and the magnetic layer, a layer containing a dye, of which the optical property changes by irradiation of energy rays, wherein in the above-mentioned layer containing a dye, continuous servo-signals based on the change of the optical property of the dye by irradiation of energy rays, are recorded on concentric tracks, and a recording/reproducing method therefor as well as an information processing apparatus. The magnetic recording medium of the present invention can be produced at a low production cost, has a large magnetically-recordable area and permits accurate tracking by a single detector.

TECHNICAL FIELD

The present invention relates to a magnetic recording medium suitablefor tracking by an optical means and a recording/reproducing methodtherefor as well as an information processing apparatus by meansthereof.

BACKGROUND ART

Floppy disk devices are used in a large quantity for informationrecording of e.g. computers or wordprocessors. Usual floppy disk deviceshad a problem that since positioning of the head is conducted by an openloop control using a step motor (control without feedback), positioningprecision is poor, and it is impossible to increase the track density.

In recent years, it has been proposed to provide grooves on a magneticrecording medium and monitoring the position of the head by reading thegroove position by an optical sensor provided integrally with the head.According to this method, positioning of the head is conducted by aclosed loop control (feedback control), whereby positioning precisioncan be improved, and it is possible to realize a track density higher byone figure than the conventional devices.

One example of a floppy disk utilizing this principle is shown in FIGS.11 and 12. Reference numeral 19 indicates a floppy disk, and FIG. 12 isan enlarged view of a part of the magnetic recording medium 4 of FIG.11. FIG. 14 is a cross-sectional view vertical to the medium plane,illustrating a servo-signal reading system of an optical trackservo-mechanism. On the surface of the magnetic recording medium 4,numerous pits 5 are formed in accordance with a track pitch. Through anaperture formed in the center of a head 6, a light from a light-emittingelement 8 is projected on the surface of the magnetic recording medium4. Tracking is carried out by reading a reflected light thereof by alight receptor 10 via an optical system 9.

An optical detector and a tracking error detecting circuit used for thispurpose are shown in FIGS. 13 and 15, respectively. In the followingdescription, P represents a track pitch.

The light receptor 10 is composed of four unit elements arranged in asquare lattice pattern and upon receiving the above-mentioned reflectedlight, outputs four signals A to D. When the head is located at thetrack position (radius R), signal B is deducted from signal A by adifferential amplifier 11 to obtain a signal proportional to cos(2πR/P).Likewise, signal D is deducted from signal C by a differential amplifier12 to obtain a signal proportional to sin(2πR/P). On the other hand,binary codes for target value T are input to address terminals of ROM 13and 14 in which a sin table and a cos table are written, to preparebinary codes representing sin(2πT/P) and cos(2πT/P). These binary codesare converted to analogue signals by multiplication type DA converters15 and 16, and at the same time, their multiplication with theabove-mentioned signals sin(2πR/P) and cos(2πR/P) obtained from theoptical detector is conducted as shown by the following formulas, andthen the difference is taken by a differential amplifier 17 whereby anerror signal is obtained by an operation as shown by the followingformulas. ##EQU1##

By feeding back this error signal to the tracking device, it is possibleto carry out tracking with high precision with an error being almost 0.Such a tracking servo-device had problems such that two sets ofdetecting devices are required, the sizes of the devices are large, andcosts required for their production are high.

A magnetic recording medium to be used for such a method is required tohave grooves (pits) preliminarily formed on its surface. As a method forforming such grooves, a method of pressing to the medium a die havingconvexes formed to correspond to the grooves, to transfer the shapes ofthe die to the medium (stamping processing) and a method of irradiatinga laser beam to decompose and remove part of the magnetic layer (laserprocessing) are known.

However, these methods have had problems such that in each case, theprocessing apparatus is extensive, a dust is generated during theprocessing and a cleaning step is therefore required, and the productioncosts are high. Further, the completed medium has grooves on its surfaceand thus has had a problem that such areas are not suitable for magneticrecording, whereby the recording capacity is reduced. Furthermore, therehas been a problem that the difference in the optical property due tothe presence or absence of such grooves is small, the detectingsensitivity is low, or it is susceptible to the influence of noises.

DISCLOSURE OF THE INVENTION

The magnetic recording medium of the present invention is a magneticrecording medium of a disk shape having a magnetic layer containing amagnetic material formed on a non-magnetic support and having, betweenthe non-magnetic layer and the magnetic layer, a layer containing a dye,of which the optical property changes by irradiation of energy rays,characterized in that, in the above-mentioned layer containing a dye,continuous servo-signals based on the change of the optical property ofsaid dye by irradiation of energy rays are recorded on concentrictracks.

The recording/reproducing method for a magnetic recording medium of thepresent invention is a recording/reproducing method for a magneticrecording medium, which comprises recording/reproducing magnetic data bymeans of a magnetic recording medium of a disk shape having a magneticlayer containing a magnetic material formed on a non-magnetic support,characterized in that using, as said magnetic recording medium, amagnetic recording medium of a disk shape having a magnetic layercontaining a magnetic material formed on a non-magnetic support andhaving, between the non-magnetic layer and the magnetic layer, a layercontaining a dye, of which the optical property changes by irradiationof energy rays, wherein in the above-mentioned layer containing a dye,continuous servo-signals based on the change of the optical property ofsaid dye by irradiation of energy rays are recorded on concentrictracks, recording/reproducing of the magnetic data is conducted whiletracking of a magnetic head is conducted by means of servo-signalsdetected by an optical means from the layer containing a dye.

The information treating apparatus of the present invention is aninformation processing apparatus for recording/reproducing magnetic datawhile tracking a magnetic head by means of servo-signals detected by anoptical means from a magnetic recording medium, characterized in that ameans is provided to read the above-mentioned servo-signals from amagnetic recording medium of a disk shape having a magnetic layercontaining a magnetic material formed on a non-magnetic support andhaving, between the non-magnetic support and the magnetic layer, a layercontaining a dye, of which the optical property changes by irradiationof energy rays, wherein in the above-mentioned layer containing a dye,continuous servo-signals based on the change of the optical property ofsaid dye by irradiation of energy rays, are recorded on concentrictracks.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view illustrating a first embodiment in which aservo-signal pattern of a magnetic recording medium of the presentinvention is read by a detector.

FIG. 2 is a schematic view illustrating a second embodiment in which aservo-signal pattern of a magnetic recording medium of the presentinvention is read by a detector.

FIG. 3 is a schematic view illustrating a third embodiment in which aservo-signal pattern of a magnetic recording medium of the presentinvention is read by a detector.

FIG. 4 is a conceptual view illustrating a state in which signals havingtwo different frequency components are recorded on tracks.

FIG. 5 is a schematic view illustrating a fourth embodiment wherein aservo-signal pattern of a magnetic recording medium of the presentinvention is read by a detector.

FIG. 6 is a schematic view illustrating a first embodiment of a devicefor writing a servo-signal pattern of a magnetic recording medium of thepresent invention.

FIG. 7 is a schematic view illustrating a second embodiment of a devicefor writing a servo-signal pattern of a magnetic recording medium of thepresent invention.

FIG. 8 is a view showing the absorbance curve of a magnetic recordingmedium prepared in Example 1.

FIG. 9 is a detailed schematic view illustrating an embodiment of apattern for writing an optical signal into a magnetic recording mediumby irradiation of energy rays.

FIG. 10 is a schematic view illustrating an embodiment of a pattern forwriting an optical signal into a magnetic recording medium byirradiation of energy rays.

FIG. 11 is a perspective view of a floppy disk.

FIG. 12 is a schematic view of an enlarged disk surface of the portion 4of FIG. 11.

FIG. 13 is a schematic view illustrating a manner in which aservo-signal pattern of a conventional magnetic recording medium is readby a detector.

FIG. 14 is a cross-sectional view illustrating a servo-signal readingsystem of a conventional optical track servo mechanism.

FIG. 15 is a block diagram of a detecting circuit of a conventionaloptical track servo mechanism.

BEST MODE FOR CARRYING OUT THE INVENTION

The magnetic recording medium of the present invention is a magneticrecording medium of a disk shape having a magnetic layer containing amagnetic material formed on a non-magnetic support and having, betweenthe non-magnetic support and the magnetic layer, a layer containing adye, of which the optical property changes by irradiation of energy rays(a dye-containing layer), characterized in that, in the above-mentioneddye-containing layer, continuous servo-signals based on the change ofthe optical property of the dye by irradiation of energy rays, arerecorded on concentric tracks.

In the magnetic recording medium of the present invention, the opticalproperty of the dye-containing layer changes by irradiation with energyrays such as laser beam, electron beam or ultraviolet rays. Accordingly,optically detectable servo-signals can easily be recorded on a medium byconducting irradiation of energy rays in correspondence withservo-signals to be recorded, whereby writing of optical signals can bedone.

As a method for irradiating energy rays to write optical signals intothe dye-containing layer, it is possible to employ a method ofirradiating a laser beam focused to have a certain spot diameter, forexample, by an optical system, or irradiating a light beam (such as astrobo light or ultraviolet rays) or an electron beam through a maskhaving light-shielding areas and light transmitting areas correspondingto the signals to be recorded.

The above-mentioned change of the optical property may, for example, bean increase of the light transmittance, a decrease of the lighttransmittance, an increase of the light reflectance or a decrease of thelight reflectance. For example, in a case where a dye, of which thelight transmittance increases by irradiation of energy rays, is used, anoptical signal can be obtained from a portion where the lighttransmittance is high in the medium surface having a low lighttransmittance. Likewise, in a case where a dye, of which the lighttransmittance decreases by irradiation of energy rays, is used, anoptical signal can be obtained from a portion where the lighttransmittance is low in the medium having a high light transmittance.

The dye to be used for the dye-containing layer is not particularlylimited so long as its optical property changes by irradiation withenergy rays and it is capable of effectively absorbing the irradiatedenergy rays, and it may optionally be selected for use.

In a magnetic recording medium, absorption of light by the magneticlayer decreases with an increase of the wavelength i.e. a ultravioletrange → a visible range → an infrared range. Accordingly, detection of atransmitted light becomes easy by employing a light within a range offrom a visible range to an infrared range. Therefore, the dye to be usedfor the dye-containing layer is preferably the one having a lightabsorption within this range, and it is preferred to irradiate a laserhaving a wavelength within this range for writing an optical signal.

In the present invention, the one having the dye incorporated in abinder resin is preferably used as the dye-containing layer. However,the color-developing properties (the absorption wavelength and theabsorbance) at that time may vary from those in an organic solvent inmany cases. Therefore, it is preferred that a dye-containing layerhaving a dye incorporated into a binder resin, is formed into a film forevaluation of the absorbance characteristics. The maximum absorptionwavelength (λmax) of the dye is preferably at least 600 nm, preferablyat least 750 nm, more preferably from 750 to 900 nm, in theabove-mentioned coated film. The reason why it is particularly preferredto employ a dye having λmax of from 750 to 900 nm, is that the change inthe absorbance can be created by utilizing a heat decomposition by acommonly used laser having a wavelength of 780 nm or 830 nm.

As the dye, various known dyes of e.g. polymethine type, cyanin type,phthalocyanin type, naphthalocyanin type, azo type, anthraquinone type,naphthoquinone type, pyrylium type, azulenium type, squarylium type,indophenol type, indoaniline type and triallylmethane type, may beemployed.

Among them, as a preferred dye, a polymethine type dye may be mentioned.As the polymethine type dye, a polymethine dye of the following generalformula (I) is particularly preferred: ##STR1## (in the general formula(I), each of R¹ to R⁴, which may be the same or different, is a hydrogenatom, a halogen atom, a hydroxyl group, a carboxyl group, or asubstituted or unsubstituted alkyl, amino, alkylamino, acyl, aryl,alkoxy, aralkyl, alkenyl or acyloxy group, X is an anion, m is 0, 1 or2, and l is 1 or 2, provided that when l is 2, the plurality of R¹, R²,R³ and R⁴ may be the same or different from each other).

In the above general formula (I), each of R¹ to R⁴, which may be thesame or different, is a hydrogen atom, a halogen atom, a hydroxyl group,a carboxyl group, or a substituted or unsubstituted alkyl, amino,alkylamino, acyl, allyl, alkoxy, aralkyl, alkenyl or acyloxy group. Thealkyl group may, for example, be a methyl group, an ethyl group, apropyl group, a butyl group or an amyl group or may further be asubstituted alkyl group such as a 2-hydroxyethyl group, a 2-sulfoethylgroup, a 2-carboxyethyl group, or an alkyl group substituted by e.g. ahalogen atom. As the amino group or the alkylamino group, amono-substituted or di-substituted amino group which is substituted bye.g. a methyl group, an ethyl group or a benzyl group, especialy adi-substituted alkyl group, is particularly preferred.

In the above general formula (I), as R¹ to R⁴, a hydrogen atom, ahalogen atom (such as chlorine), an alkoxy group (such as a methoxygroup or an ethoxy group), an amino group or an alkylamino group ispreferred, and a dialkylamino group is particularly preferred.

In the above general formula (I), X is an anion, and for example, ClO₄,BF₄, CH₃ C₆ H₄ SO₃, Cl or I may be mentioned.

The content of the dye in the dye-containing layer varies depending uponthe type of the dye to be used, the thickness of the dye-containinglayer, the performance of the light signal detector, etc., but may besuch an amount that the light transmittance, the light reflectance orthe like changes to a measurable extent by irradiation of energy rays.It is usually from 0.001 to 30 wt % in the dye-containing layer.

The dye-containing layer may contain additives such as an antistaticagent, a deterioration-preventing agent and a crosslinking agent withina range not to impair the effects of the present invention.

The dye-containing layer is formed between the non-magnetic support andthe magnetic layer. Especially, in the present invention, thedye-containing layer is formed between the non-magnetic support and themagnetic layer, and in that dye-containing layer, continuousservo-signals based on the change on the optical property of the dye byirradiation of energy rays, will be recorded on concentric tracks.

As a method for forming the dye-containing layer between thenon-magnetic support and the magnetic layer, a method may, for example,be mentioned wherein a dye solution having a dye dissolved or dispersedin a solvent, is a mixed with a binder resin, a dispersant, etc., as thecase requires, to prepare a coating solution, which is coated directlyor with another layer interposed, on the non-magnetic support beforeformation of the magnetic layer. As the coating method, commonly usedvarious coating methods such as air doctor coating, blade coating,reverse roll coating and gravure coating, may be employed. Further,coating may be conducted by a method such as vapor deposition ortransfer. As the resin, the solvent or the like to be used for thepreparation of the coating solution, conventional materials may be usedalone or in combination as a mixture, as will be described hereinafter.

As the non-magnetic support, a polyester such as polyethyleneterephthalate or polyethylene naphthalate is usually employed in view ofthe excellent mechanical properties, heat resistance, electricalproperties and chemical resistance. However, such a polyester film ispoor in the adhesive property with the magnetic layer, since it has ahigh degree of crystal orientation. Therefore, in order to improve theadhesive property between the non-magnetic support and the magneticlayer, treatment with a surface modifier such as an alkali, an aqueousamine solution, trichloroacetic acid or a phenol may sometimes beapplied to the surface of the non-magnetic support. In such a case, adye may be mixed to the surface modifier, and a such a mixture may becoated on the non-magnetic support.

Further, an easily adhesive layer may sometimes be formed by means ofvarious easily adhesive resins in order to improve the adhesion betweenthe non-magnetic support and the magnetic layer. In such a case, a dyemay be incorporated in such an easily adhesive layer. For example, amaterial having a dye blended to a conventional adhesive resin such asan acrylic resin, a polyurethane resin or a polyester resin may,usually, be adjusted as a coating solution, which is then coated on themagnetic layer side surface of the non-magnetic support. The thicknessof the easily adhesive layer is usually from 0.005 to 5 μm as a dry filmthickness.

Further, an interlayer containing an electrically conductive materialand a binder resin may be formed between the magnetic layer and thenon-magnetic support in order to improve the electrification property ofthe magnetic layer. In such a case, a method of incorporating a dye insuch an interlayer, may be mentioned.

As the electrically conductive material, an electrically conductivemetal powder or a metal compound may, for example, be mentioned. Forexample, a powder of a metal such as silver or platinum, or a powder ofa metal compound such as tin oxide, zinc oxide or potassium titanate,may be used, although the electrically conductive material is notparticularly limited. The average particle size of such a powder ispreferably from 0.005 to 0.6 μm. With the magnetic recording mediumprovided with such an electrically conductive interlayer containing adye, the electric resistance of the surface of the magnetic layer islow, and the amount of carbon black in the magnetic layer can bereduced, whereby it will be excellent in the light transmittance andsuitable for writing and reproduction of light servo-signals. Thethickness of such an interlayer is usually from 0.005 to 5 μm as a dryfilm thickness.

As elements other than the dye in the magnetic recording medium of thepresent invention, conventional materials may be used.

As the magnetic material to be used for the magnetic layer, variousferromagnetic powders including a powder of a ferromagnetic metal suchas Fe, Ni or Co, or a magnetic alloy containing such a ferromagneticmetal as the main component, such as Fe, Ni, Co, a Fe-Co alloy, a Fe-Nialloy, a Fe-Co-Ni alloy, a Fe-Ni-Zn alloy, a Fe-Co-Ni-Cr alloy or aCo-Ni alloy, an iron oxide magnetic powder such as γ-Fe₂ O₃, Fe₃ O₄,Co-containing γ-Fe₂ O₃ or Co-containing Fe₃ O₄, and a metal oxide typemagnetic powder such as CrO₂, barium ferrite or strontium ferrite, maybe mentioned. From the viewpoint of the light transmittance, etc.,barium ferrite is particularly preferred.

The amount of the magnetic material to be used, is preferably such thatthe content in the magnetic layer will be from 50 to 90 wt %,particularly from 55 to 85 wt %, as the amount of the ferromagneticpowder.

As the binder resin to be used for the magnetic layer, the one which isexcellent in the adhesion with the support and in the abrasionresistance, is suitably used. For example, a polyurethane resin, apolyester resin, a cellulose derivative such as a cellulose acetatebutyrate, cellulose diacetate or nitrocellulose, a vinyl chloride typeresin such as a vinyl chloride-vinyl acetate copolymer, a vinylchloride-vinylidene chloride copolymer or a vinyl chloride-acryliccopolymer, various synthetic rubbers such as a styrene-butadienecopolymer, an epoxy resin or a phenoxy resin may be mentioned. Theseresins may be used alone or in combination as a mixture of two or moreof them.

The binder resin is preferably used so that the content in the magneticlayer would be from 2 to 50 wt %, particularly from 5 to 35 wt %.

In the magnetic coating material, a low molecular weight polyisocyanatecompound having a plurality of isocyanate groups, may be incorporated,so that a three dimensional network structure will be formed in themagnetic layer to improve the mechanical strength. As such a lowmolecular weight polyisocyanate compound, a trimethylol propane adductof tolylenediisocyanate may, for example, be mentioned. Such a lowmolecular weight polyisocyanate compound is preferably used in an amountof from 5 to 100 wt % relative to the binder resin.

Further, to the magnetic coating material to form the magnetic layer,various additives such as a lubricant, an abrasive agent, an antistaticagent, a dispersant, etc., may be incorporated, as the case requires.

Here, as the lubricant, various lubricants of e.g. an aliphatic type, afluorine type, a silicone type or a hydrocarbon type, may be used. Asthe aliphatic lubricant, a fatty acid, a metal salt of a fatty acid, afatty acid ester, a fatty acid amide or an aliphatic alcohol may, forexample, be mentioned. As the fatty acid, oleic acid, lauric acid,myristic acid, palmitic acid, stearic acid or behenic acid may, forexample, be mentioned. As the metal salt of a fatty acid, a magnesiumsalt, an aluminum salt, a sodium salt or a calcium salt of such a fattyacid may, for example, be mentioned. As the fatty acid ester, a butylester, an octyl ester or a glyceride of the above-mentioned fatty acidmay, for example, be mentioned. As the fatty acid amide, an amide of theabove-mentioned acid as well as linolic acid amide or caproic acid amidemay, for example, be mentioned. As the aliphatic alcohol, laurylalcohol, myristyl alcohol, palmityl alcohol, stearyl alcohol or oleylalcohol may, for example, be mentioned. As the fluorine type lubricant,a perfluoroalkyl polyether or a perfluoroalkyl carboxylic acid may, forexample, be mentioned. As the silicone type lubricant, silicone oil ormodified silicone oil may, for example, be mentioned. Further, a solidlubricant such as molybdenum disulfide or tungsten disulfide, or aphosphoric acid ester may, for example, be used. As the hydrocarbon typelubricant, paraffin, squalane or wax may, for example, be mentioned. Theamount of the lubricant to be used is usually such that the content inthe magnetic layer is within a range of from 0.1 to 20 wt %, preferablyfrom 1 to 10 wt %. In a case where the magnetic layer is formed in twolaminated layers, the content of the lubricant may be varied between theupper layer and the lower layer.

As the abrasive agent, alumina, molten alumina, corandom, siliconecarbide, chromium oxide or silicone nitride may, for example, bementioned. Among them, relatively hard material is preferably used. Thenumber average particle size is preferably at most 2 μm. The amount ofthe abrasive agent to be used is preferably such that the content in themagnetic layer is within a range of from 1 to 20 wt %.

As the antistatic agent, a natural surfactant such as carbon black,graphite or saponin, a non-ionic surfactant such as an alkylene oxidetype or a glycerine type surfactant, a cationic surfactant such as ahigher alkylamine type, a quaternary ammonium salt type, pyridine orother heterocyclic type surfactant containing an acid group such as acarboxylic acid group, a sulfonic acid group, a phosphoric acid group, asulfuric acid ester group or a phosphoric acid ester group, anamphoteric surfactant such as an amino acid type, an amino sulfonic acidtype, a sulfuric acid or phosphoric acid ester of an amino alcohol typesurfactant may, for example, be used. These surfactants may be usedalone or in admixture. The amount of the antistatic agent to be used isusually such that the content in the magnetic layer is within a range offrom 1 to 15 wt %. These materials are those useful as antistaticagents, but in some cases, they may be used for the purpose of improvingthe dispersibility or the lubricating property.

As the dispersant, a C₁₂₋₁₈ fatty acid such as capric acid, lauric acid,myristic acid, oleic acid or linolic acid, a metal soap composed of analkali metal or alkaline earth metal salt of such a fatty acid, orlecithin, may, for example, be used. The amount of the dispersant isusually such that the content in the magnetic layer is within a range offrom 0 to 20 wt %.

As the solvent to be used for kneading, dispersing or coating themagnetic coating material, a ketone such as methyl ethyl ketone, methylisobutyl ketone or cyclohexanone, an alcohol such as methanol, ethanol,propanol or isopropyl alcohol, an ester such as methyl acetate, ethylacetate or butyl acetate, an ether such as diethyl ether ortetrahydrofuran, an aromatic hydrocarbon such as benzene, toluene orxylene, or an aliphatic hydrocarbon such as hexane, may, for example, bementioned.

With respect to the method for kneading or dispersing, or the order ofadding the respective components, conventional methods commonly used forkneading or dispersing the magnetic coating material, may be employed.

As the non-magnetic support, various plastics such as, a polyester suchas polyethylene terephthalate or polyethylene naphthalate, a polyolefinsuch as polypropylene or polyethylene, a cellulose derivative such ascellulose acetate, polycarbonate, polyamide and polyimide, may, forexample, be used.

As a method for coating the magnetic coating material directly or withanother layer interposed, on the non-magnetic support, various methodscommonly used, such as air doctor coating, blade coating, reversecoating and gravure coating, may be employed. In a case where magneticcoating materials are coated in a plurality of layers, the coatingsolution of the lower layer and the coating solution for the upper layermay simultaneously be coated in wet states, or the respective layers maysequentially be coated. The thickness of the magnetic layer is usuallyfrom 0.1 to 10 μm, preferably from 0.3 to 2 μm, as the thickness afterdrying.

Further, a top coating layer for imparting a lubricating property or aback coating layer for antistatic purpose may be formed.

Further, if necessary, orientation treatment, random treatment orsmoothing treatment may be carried out.

The magnetic recording medium of the present invention is characterizedin that in the dye-containing layer formed between the non-magneticsupport and the magnetic layer, continuous servo-signals based on thechange of the optical property of the dye by irradiation of energy rays,are recorded on concentric tracks.

Servo-signals may be recorded by forming areas where the opticalproperty of the dye has changed by irradiation of energy rays, on theconcentric tracks of the dye-containing layer. The areas where theoptical property of the dye has changed, may be continuously formed onthe tracks, or an area where the optical property of the dye has changedand an area where no such change has occurred may be formed alternately.Further, the areas where the optical property of the dye has changed maybe formed so that signals containing one type of a frequency componentare obtained as the servo-signals, or the areas where the opticalproperty of the dye has changed, may be formed so that signalscontaining two types of frequency components, may be obtained.

Here, the case where the areas in which the optical property of the dyehas changed, are provided so that signals containing two types offrequency components, may be obtained as the servo-signals, will bedescribed in detail.

The signals containing two types of frequency components as theservo-signals may be recorded on one servo track, or two types ofsignals differing in the frequency may respectively be recorded atspatially different close positions. In the latter case, the two signalsmay be detected simultaneously by means of a single detector, whereby itis possible to obtain signals having two types of frequency componentssuperposed on each other. The servo-signals read by an optical means bythe detector, will be separated into the respective frequency componentsby a frequency separating means, and from such frequency components, anerror signal for detecting a tracking error, can be obtained, wherebyaccurate tracking will be possible.

The above-mentioned respective frequency components are recorded so thatthey have sequentially mutually different phase servo-signals among therespective servo-tracks. In such a case, the present head position canbe detected by measuring the phase servo-signals, and the head positioncan be controlled so that the measured values will be the prescribedvalues.

FIG. 1 illustrates one embodiment of the magnetic recording medium ofthe present invention, and shows the manner of reading a signal 21having a long wavelength and a signal 22 having a short wavelength by adetector 31. In the embodiment illustrated in FIG. 1, signals 21 and 22are recorded at different close positions on the surface of the medium.The signals thus recorded to be close to each other will be mixed at thetime of the reproduction, and a signal representing the sum of the twowill be output from the detector. The wavelength of the signal 22 isadjusted to be 1/2 of the wavelength (λ) of the signal 21, and thesignals are recorded so that the phase of the signal 21 is sequentiallydifferent from one track to the next. In FIG. 1, the signals arerecorded so that the phase difference between the signal 21 and thesignal 22 will sequentially be different such that it is 0 in track 3 asshown at b, λ/8 in track 2 as shown at a and λ/4 in track 1 as shown atc. Of course, the phase difference sequentially provided among thetracks may optionally be selected, and phase differences both amongsignal 21 and among signal 22 may be provided among the tracks.

A shows a case where the detector 31 is located just above track 2. Inthis case, the signal d output by the detector 31 corresponds to thesignal of track 2. If the detector moves upward and arrives at theposition shown at B, a signal of track 3 will be mixed to the signal dof the detector, and the phase of the short wavelength componentadvances. Inversely, if the detector 31 moves downwardly and arrives atthe position shown at c, the signal of track 1 will be mixed to thesignal d of the detector, and the phase of the short wavelengthcomponent delays. Thus, the position of the detector can be detected asa phase difference. As the phase difference of the short wavelengthcomponent can thus be detected, accurate tracking can be conducted bymoving the head so that the phase difference thus detected will fallwithin a predetermined range.

However, in a case where such two types of signals having differentfrequencies are to be recorded at spatially different close positions,respectively, a plurality of scanning will be required to writeservo-signals in one track. Whereas, in a case where signals containingtwo types of frequency components are to be recorded on one servo-track,writing of servo-signals in one track can be carried out by a singlescanning.

As a method for recording signals containing two types of frequencycomponents on one servo track, there may, for example, be mentioned amethod wherein trigonometric functions corresponding to the two types ofsignals are added, and the added size is analogically recorded incorrespondence with the width of the servo track or it is converted intobinary signals by PWM (pulse width modulation) and recorded, or a methodwherein the servo track is divided into fine sections in acircumferential direction, and the respective frequency components willbe sequentially recorded in the corresponding different recordingsections.

FIG. 2 is a schematic view illustrating an enlarged part of oneembodiment of a magnetic recording medium of the present invention inwhich servo-signals are recorded by changing the widths of the servotracks. Along the circumferential direction of the magnetic recordingmedium, servo tracks 0 and 1 are provided. In FIG. 2, the areas shown bywidely spaced oblique lines represent recorded areas in the tracks, andsuch areas are different from other areas in the optical properties suchas the light reflectance and light transmittance. Other servo tracks arelikewise provided, although they are not shown. The width of a servotrack corresponds to the intensity of the signal 20 (biased and includesa constant portion), and said signal 20 is a combined signal of aplurality of frequency components i.e. a combined signal of the signal21 having a long wavelength and the signal 22 having a short wavelength.In FIG. 2, the signals 21 and 22 are shown simply for the convenience ofexplanation. In reality, only their combined signal 20 is recorded.

FIG. 3 is a schematic view illustrating an enlarged part of oneembodiment of the magnetic recording medium of the present invention inwhich servo-signals obtained by PWM modulation are recorded. In FIG. 3,the areas shown by black areas represent recorded areas in the tracks,and their widths in the circumferential direction correspond to thepulse widths of the signals obtained by PWM modulation. The recordedareas are different from other areas in the optical properties such asthe light reflectance and the light transmittance.

FIG. 4 is a conceptual view illustrating a manner in which two signalshaving different frequencies are recorded in servo track 0 and servotrack 1 on a magnetic recording medium. The signal 20 has as itsfrequency components a signal 21 having a long wavelength and a signal22 having a short wavelength. In FIG. 4, the signals 21 and 22 are shownsimply for the purpose of explanation, and in reality, only the signal20 as their combined signal is recorded as modulated by PWM, as shown inFIG. 3.

In FIGS. 2 and 4, the signals 21 and 22 have common wavelengths λ andλ/2, respectively, in the respective tracks. However, there is noparticular restriction as to these wavelengths. The wavelengths mayoptionally be determined depending upon the required responsecharacteristics, etc. Further, between the signals 21 and 22, adifferent phase difference is sequentially provided from one track tothe next. Namely, in FIG. 2, the signal 21 has the same phase in tracks0 and 1, whereas the signal 22 has a phase difference of δ betweentracks 0 and 1. In such a manner, by setting the phase of the signal 21to be equal in all tracks while sequentially differentiating the phaseof the signal 22 by δ, the phase difference between the signals 21 and22 will sequentially be different by δ from one track to the next. Ofcourse, there is no particular restriction as to the value for δ, and itmay optionally be selected. Otherwise, phase differences both among thesignals 21 and among the signals 22 may be provided among tracks.

FIG. 5 is a schematic view illustrating an enlarged part of oneembodiment of a magnetic recording medium of the present invention inwhich a plurality of frequency components are, respectively, recorded inthe sections divided in the circumferential direction on the servotracks.

FIG. 5 shows a manner in which optical signals having two types offrequency components i.e. the signal 21 having a long wavelength and thesignal 22 having a short wavelength, which are recorded in the servotracks 0 to 3 formed in the circumferential direction, are read from adetection site 31.

In the embodiment shown in FIG. 5, the servo tracks are divided in finesections in the circumferential direction so that the areas forrecording the two types of frequency components i.e. the signals 21 and22, are formed alternately. In FIG. 5, 1 shown above indicates a sectionin which the signal 21 having a long wavelength is to be recorded, and 2indicates a section in which the signal 22 having a short wavelength isto be recorded. 1 and 2 are divided in the circumferential direction andalternately formed. In track 1, with respect to the positions 1 at whichthe signal 21 is to be recorded, continuous 8 sections from position 0in the circumferential direction are in a recorded state (shown by ablack area in the Figure), and the following 8 sections are blanc (shownby a blanc area in the Figure). By sequentially repeating such arecording pattern, a signal having a wavelength shown by λ in the Figurewill be obtained. With respect to the positions 2 at which the signal 22is to be recorded, in track 1, continuous four sections from distance 0are blanc, and the following four sections are continuously in arecorded state, then, the subsequent four sections are likewise blanc,and four sections are in a recorded state. By repeating this recordingpattern sequentially, a signal having a wavelength of λ/2 will beobtained.

The signals 21 and 22 have common wavelengths λ and λ/2, respectively,in the respective tracks. However, there is no particular restriction asto these wavelengths, and they may optionally be selected depending uponthe desired response characteristics, etc. Further, between the signals21 and 22, sequentially different phase difference is provided from onetrack to the next. Namely, in FIG. 5, the signal 21 has the same phasein tracks 0 to 3, whereas the signal 22 has the phase sequentiallychanged by λ/8 among the tracks 0 to 3, whereby the phase differencebetween the signals 21 and 22 will be sequentially different by λ/8 fromone track to the next. Of course, the difference in the phase differencesequentially provided from one track to the next is not limited to λ/8and may optionally be selected. Further, phase differences both amongthe signals 21 and among the signal 22 may be provided among the tracks.

The widths of the sections divided in the circumferential direction onthe servo tracks may simply be sufficiently be smaller than thewavelength of the respective frequency components, and by setting thewidths of the sections to be adequately smaller than the detection rangeof the detector, a signal having the respective frequency componentscombined will be output from the detector. With magnetic recording mediashown in FIGS. 1 to 5, tracking is conducted, for example, as follows. Adetector, not shown, is integrally formed with a magnetic head, notshown, and detects a reflected light or a transmitted light from thedetection region 31 by irradiation of light rays from a light source,not shown. Which one as between the reflected light and the transmittedlight is to be detected, is determined depending upon which opticalproperty as between the reflectance and the transmittance was utilizedfor recording on the servo tracks of the substrate. The optical propertyis different between the recorded areas and the non-recorded areas inthe servo tracks, whereby the quantity of light received by the detectorby the rotation of the magnetic recording medium will periodicallychanges, and an alternate signal will be output from the detector.

Here, in the case of a magnetic recorking medium of the presentinvention in which servo-signals modified by PWM are recorded, thedetection region 31 is adequately larger than the modulation cycle byPWM, whereby the recorded signals in this region are averaged foroutput, whereby an optical record by PWM with and adequately highfrequency will be detected as a signal which changes in an analoguefashion. Accordingly, the alternate signal output from the detector willbe substantially the same signal as the signal 20. When the detectionarea is small, the signal of the PWM-modulation frequency will becontained in the output signal of the detector. In such a case, it canbe removed by means of e.g. an electron filter.

The detected alternate signal has two frequency components i.e. thesignals 21 and 22, which can be separated by means of a frequencyseparation means such as a band pass filter. As mentioned above, thephase difference between the signals 21 and 22 sequentially differs by δfrom one track to the next, whereby the present position of the magnetichead can be detected by measuring the phase difference between theseparated respective frequency components by e.g. a phase differencedetector. Namely, when the magnetic head has an error relative to thecenter of the track, the servo-signal of the adjacent track will bemixed in proportion to the error. At that time, the phase differencebetween the signals 21 and 22 differs by δ between the adjacent tracks,whereby the phase difference to be detected will be an intermediatevalue corresponding to the above error. Therefore, by controlling theposition of the magnetic head so that this phase difference will be theprescribed value, accurate tracking will be possible.

Various conventional apparatus may be employed as the servo apparatusfor tracking. A servo circuit generally known as PLL (phase locked loop)is a servo circuit using the phase difference as the signal source,whereby accurate tracking can be carried out by controlling the headposition by PLL, so that the phases of signals obtained by multiplyingthe above-mentioned two signals, respectively, by multiplicationcircuits so that the short wavelength component is multiplied fourtimes, and the long wavelength component is multiplied 8 times, willagree to each other. Further, in a case where a servo apparatus isconstructed using a digital signal processor, the rise times of theabove-mentioned two signals are read by a digital signal processor, andtheir difference is computed to readily obtain a tracking error.

In the present invention, the above-mentioned servo-signals will berecorded by forming in a magnetic recording medium areas where anoptical property such as light reflectance or light transmittance islocally different. As a method for recording servo-signals on theabove-mentioned magnetic recording medium, it is possible to employ, forexample, a method of irradiating a laser beam at a certain specifiedposition on the surface of the magnetic recording medium or irradiatinga light beam (such as a strobo light or ultraviolet rays) or an electronbeam through a mask having light shielding areas and light-transmittingareas corresponding to the signals to be recorded. At the areas wherethe light is irradiated, the optical property such as the lightreflectance or light transmittance will change due to the chemicalchange of the dye preliminarily incorporated in the magnetic recordingmedium, and such areas will be in a recorded state.

FIG. 6 is a schematic view illustrating an embodiment of a methodsuitable for recording servo-signals. In FIG. 6, reference numeral 30indicates a laser generator which generates a laser beam 45 underexcitation by a powder source apparatus, not shown. Reference numeral 32is AOM (accousto-optical modulator), which has a function of diffractingor deflecting the laser beam by a compressional wave in a crystal whichis formed by applying a supersonic wave to the crystal placed in theoptical path. By AOM 32, the diffraction angle changes due to thewavelength of the applied supersonic wave, and the amount of diffractionchanges due to the intensity. This apparatus is constructed so that theamount of diffraction is controlled by changing the intensity ofgeneration by the signals applied to the generator 33. The laser beampassed through AOM 32 is changed in its direction by a mirror 35provided on a movable carriage of a linear motor 34 and then focused byan objective lens 36 provided on the above-mentioned movable carriageand irradiated to the magnetic recording medium 37. The magneticrecording medium 37 is rotated by a spindle motor 38, and the rotationalangle is transmitted to the control apparatus 39. The control apparatus39 is designed so that the focused area is set at a predetermined radialposition by sending a signal to the linear motor 34, and then dependingupon the rotational angle of the spindle motor, a signal for theintensity of the laser beam is sent to the generator 33 based on thepredetermined pattern. The area of the magnetic recording medium wherethe laser beam is focused, will be heated, and the optical property suchas the light reflectance or light transmittance will change due to e.g.a chemical change of the dye in the dye-containing layer, to form aservo track. This operation is repeated to obtain a necessary number oftracks, whereby optical signals will be recorded on the magneticrecording medium.

FIG. 7 is a schematic view illustrating another embodiment of a methodsuitable for recording servo-signals. Reference numeral 40 indicates anultraviolet light source, and numeral 41 indicates a mask. The mask 41is the one in which patterns corresponding to writing signals arepreliminarily formed by such a means as photoetching. Numeral 42indicates a magnetic recording medium having a dye-containing layer, ofwhich the optical property changes by irradiation of ultraviolet rays.This can be accomplished, as mentioned above, by incorporating a dye ina specific layer of the medium. The magnetic recording medium 42 willpass through an ultraviolet ray irradiation area 44 by a transportingmeans 43 at a predetermined speed in such a state that the mask 41 isoverlaid thereon. As a result, the optical property of the medium suchas the light reflectance or light transmittance, will change dependingupon the shapes of the light transmitting areas of the mask 41, wherebyoptically readable signals will be recorded.

Further, a method of carrying out the above-described method by means ofan electron beam, is particularly effective. On a thin metal plate whichdoes not permit transmittance of an electron beam, such as a thinstainless steel plate having a thickness of about 10 μm, a patterncorresponding to servo-signals will be formed, and this is used as amask. This mask is overlaid and centerized on a magnetic recordingmedium prepared by forming a dye-containing layer and a magnetic layeron a support, followed by stamping into a disk shape, attaching a hubthereto followed by centering, and then an electron beam is irradiated.The electron beam passes through the magnetic layer to form a desiredservo pattern in the dye-containing layer.

When a laser or ultraviolet beam is employed, it is preferred that afterforming the dye-containing layer on the substrate, the mask pattern isoverlaid thereon, followed by irradiation with the laser or ultravioletbeam, and then the magnetic layer is formed. At the areas irradiatedwith energy rays, the optical property changes due to e.g.discoloration, whereby servo-signals will be formed.

At the time of reading servo-signals, it is possible to read them fromthe magnetic layer side in a case where the magnetic layer is made of alight transmitting material such as barium ferrite. On the other hand,if the light transmittance is insufficient, it is preferred to read themfrom the opposite side through the substrate. The magnetic layer may beprovided on each side of the medium.

Further, additional signals may be recorded in the dye-containing layerso that optical reading other than servo-signals can be conducted. Suchadditional signals may be any signals so long as they have frequenciesdifferent from the servo-signals, and their number may be increased solong as the frequency separating means will permit. Further, theadditional signals may be recorded as combined signals on the same servotracks as for the servo-signals, or may be recorded at spatiallydifferent close positions.

Such additional signals may be used for recording e.g. informationidentifying the medium itself, information specifying the position inthe rotational direction of the medium such as a sector number, orinformation for specifying the position in the radial direction of themedium such as a track number.

Such additional signals may be recorded in a dye-containing layer formedother than between the non-magnetic support and the magnetic layer. Sucha dye-containing layer may be formed on the magnetic layer or on anon-magnetic support on the side where no magnetic layer is formed inthe case where the magnetic layer is formed only on one side. Otherwise,a dye may be incorporated in the magnetic layer, so that the magneticlayer serves also as a dye-containing layer, or a dye may beincorporated in a non-magnetic support so that the non-magnetic supportserves also as a dye-containing layer.

In a case where a dye-containing layer is to be formed on the magneticlayer, after coating a magnetic layer on a non-magnetic support, adye-containing solution is coated on the surface directly or withanother layer interposed, followed by drying. Further, thisdye-containing coating layer may be used as or in combination withanother coating layer for the purpose of lubricating or protecting themagnetic layer.

For example, in a case where it is used as a fluorine compound coating,a solution having a dye added to a suspension of a fluorinatedhydrocarbon polymer such as tetrafluoroethylene teromer,ethylene-tetrafluoroethylene copolymer or hexafluoropropylene polymer,may be coated on the magnetic layer. Such a construction wherein anothercoating layer is used as a dye-containing layer, is preferred andadvisable from the economical viewpoint.

As a method for forming a dye-containing coating layer, variousconventional coating methods may be employed such as air doctor coating,blade coating, reverse roll coating and gravure coating.

In a case where a dye is to be incorporated in the magnetic layer, a dyemay be added at the time of the preparation of a magnetic coatingmaterial containing a magnetic material, binder resin, etc., followed bykneading and dispersing.

In a case where a dye is to be incorporated in the non-magnetic support,it is common to knead a dye into a raw material resin at the time ofpreparation of a resin film such as a polyester to be used as thenon-magnetic support, or a conventional blending method may be appliedso that a dye is added at the time of preparing the raw material resin.

Now, specific embodiments of the present invention will be described infurther detail with reference to Examples. However, it should beunderstood that the present invention is by no means restricted by thefollowing Examples.

EXAMPLE 1

On a polyethylene terephthalate film having a thickness of 75 μm, asolution of a Ni-containing indoaniline dye of the following structuralformula (II) was coated to form a dye-containing interlayer in athickness of about 0.2 μm as dry thickness. ##STR2##

The Ni-containing indoaniline dye off the structural formula (II) has apeak of absorbance in the vicinity of 780 nm, and when heated to atemperature of from 200° to 400° C., it decomposes, whereby the abovepeak decreases to a negligible level.

Then, a magnetic coating material prepared by mixing 74 parts by weightof barium ferrite powder, 10 parts by weight of a polyurethane resin, 2parts by weight of a phosphoric acid ester, 7 parts by weight ofaluminum oxide, 1 part by weight of carbon black and 5 parts by weightof butyl stearate in tetrahydrofuran, was coated in a thickness of about0.5 μm as dry thickness, to obtain a magnetic recording medium.

The absorption curve of the magnetic recording medium thus prepared, isshown by a solid line in FIG. 8. In the Figure, the curve shown by adotted line is the absorbance curve of a magnetic recording mediumhaving no dye incorporated. The dye-containing magnetic recording mediumhas a peak of absorbance in the vicinity of 780 nm which is thewavelength of a semiconductor laser employed for detecting records. Bylocal irradiation of energy rays (such as irradiation of a semiconductorlaser with a high output power, the dye is locally decomposed anddiscolored, whereby the absorbance of that area will be substantiallyequal to the absorbance of the magnetic recording medium containing nodye. This diference is extremely large, and as shown in FIG. 8, thetransmittance at 780 nm is 2% when the dye is contained, whereas itchanges largely to 17% when no dye is contained. Accordingly, therecorded signals can easily be read by means of a semiconductor laserwith a low output power.

An embodiment of a pattern for writing optical signals by irradiation ofenergy rays is shown in FIGS. 9 and 10. In an actual system, the pitchof the recorded signals is at a level of from 5 μm to 10 μm. However, inthis Figure, the pitch is shown as enlarged in order to facilitate theunderstanding.

In each track (represented by i in FIG. 9), an optical record area a_(i)having a short record wavelength λa and an optical record area b_(i)having a long record wavelength λb (λb=2λa) are provided, and opticalrecords b have the same phase among the respective tracks, and opticalrecords a have phases which differ by λa/4 from one track to the next.

In FIG. 9, the light transmittance at the area shown by the obliquelines, is measured by a light detector integrally formed with a magnetichead. As the disk rotates, an alternate signal will be output from thedetector. Since optical records having two types of wavelengths areprovided, the output signal contains signals for two types offrequencies. The high frequency component generated by optical records aundergoes a phase change as the detector moves across the track, whereasthe phase of the low frequency component generated by optical records bwill remain constant. Accordingly, by separating the respectivefrequency components by a band path filter and measuring the phasedifference between the two frequency components, the head position willbe determined, and accurate tracking can be carried out by controllingthe head position so that the phase difference will be the predeterminedvalue.

To the above-mentioned magnetic recording medium, a semiconductor laserwith a high output power is locally irradiated to record optical signalshaving a pattern as shown in FIGS. 9 and 10. Reading of the opticalsignals was conducted by means of a semiconductor laser with a lowoutput power.

EXAMPLE 2

On a polyethylene terephthalate film having a thickness of 75 μm, aneasily adhesive layer having the Ni-containing indoaniline dye of theabove-mentioned structural formula (II) blended to an acrylurethane typeadhesive resin, was formed in a thickness of about 0.2 μm as drythickness. Then, a magnetic coating material prepared by mixing 74 partsby weight of barium ferrite powder, 10 parts by weight of a polyurethaneresin, 2 parts by weight of a phosphoric acid ester, 7 parts by weightof aluminum oxide, 1 part by weight of carbon black and 5 parts byweight of butyl stearate in tetrahydrofuran, was coated in a thicknessof about 0.5 μm as dry thickness, to obtain a magnetic recording medium.

The absorbance of the magnetic recording medium thus prepared, wasmeasured, whereby it showed an absorbance curve similar to the one shownin FIG. 8.

To the above-mentioned magnetic recording medium, a semiconductor laserwith a high output power was locally irradiated, whereby optical signalshaving a pattern as shown in FIGS. 9 and 10, were recorded. Reading ofthe optical signals was carried out by means of a semiconductor laserwith a low output power.

EXAMPLE 3 ##STR3##

A methyl ethyl ketone solution containing 4 parts by weight of apolymethine type dye (λmax=about 820 nm) of the above structural formula(III), 72 parts by weight of a vinyl chloride/vinyl acetate/vinylalcohol copolymer (VAGH, manufactured by Union Carbide) and 24 parts byweight of polyisocyanate, was prepared, and this solution was coated onone side of a polyethylene terephthalate film having a thickness of 75μm, and the resin was cured by maintaining it at 60° C. for three daysto form a dye-containing layer. The thickness of the dye-containinglayer was about 1 μm, and the absorbance at λmax was about 1.0.

Then, to impart electrical conductivity to this film, a coating materialcontaining 100 parts by weight of tin oxide powder (particle size: 0.03μm), 15 parts by weight of a binder resin and 180 parts by weight of anorganic solvent (methyl ethyl ketone/cyclohexanone=1/1), was prepared,and this coating material was coated on each side of the above film sothat the film thickness after drying would be 0.5 μm. Further, amagnetic coating material comprising 100 parts by weight of bariumferrite magnetic powder, 4 parts by weight of a vinyl chloride-vinylacetate copolymer, 4 parts by weight of polyurethane, 2 parts by weightof polyisocyanate, 1 part by weight of carbon black, 5 parts by weightof alumina, 5 parts by weight of butyl stearate and 280 parts by weightof an organic solvent (methyl ethyl ketone/cyclohexanone=1/1), waskneaded and dispersed by a ball mill to obtain a coating solution, whichwas then coated on each side of the above coated film, so that the layerthickness after drying would be 0.8 μm.

The surface smoothing treatment was carried out by calendar treatment,and then it was punched out into a 3.5 inch disk. Thereafter, the dyewas partially decomposed and discolored by a semiconductor laser with awavelength of 830 nm to obtain a pattern as shown in FIGS. 9 and 10. Thelight transmittance of 830 nm was about 11% at the areas where the dyewas not decomposed. Whereas, the light transmittance at the decomposedareas was about 2%. By arranging the decomposed areas along the tracksin the circumferential direction, the above-mentioned servo informationwas recorded on a floppy disk.

INDUSTRIAL APPLICABILITY

With the magnetic recording medium of the present invention, specificservo-signals are recorded in a dye-containing layer suitable forwriting signals by energy rays, whereby writing is possible with anenergy dose relatively small as compared with conventional method ofwriting signals, and an inexpensive writing apparatus can be employed.Further, there will be no removal of material attributable to writing,and no dust or the like will be generated, whereby no cleaning stepafter writing will be required. Further, writing of signals by energyrays, does not adversely affect the magnetic recording material, and theareas where signals are written by energy rays, can be used for magneticrecording. Furthermore, the change of the optical property of the dye byirradiation of energy rays is large, and the signals can be detectedwith a high sensitivity.

Further, with the magnetic recording medium of the present invention,the head position can be measured by a single detector, whereby theapparatus can be down-sized, and the production costs can be reduced.

We claim:
 1. A magnetic recording medium of a disk shape having amagnetic layer containing a magnetic material formed on a non-magneticsupport and having, between the non-magnetic layer and the magneticlayer, a layer containing a dye, of which the optical property changesby irradiation of energy rays, characterized in that, in the dyecontaining layer, continuous servo-signals based on the change of theoptical property of said dye by irradiation of energy rays are recordedon concentric tracks, wherein the continuous servo-signals recorded onthe concentric tracks contain signals having two signals with differentwavelengths superposed on each other, and said two signals are uniform,respectively, and the phase difference between said two signals differssequentially from one track to the next.
 2. The magnetic recordingmedium according to claim 1, wherein the layer containing a dye, is alayer having a dye compound dispersed in a binder resin.
 3. The magneticrecording medium according to claim 1, wherein the layer containing adye, is electrically conductive.
 4. The magnetic recording mediumaccording to claim 3, wherein the layer containing a dye, contains anelectrically conductive substance.
 5. The magnetic recording mediumaccording to claim 4, wherein the electrically conductive substance istin oxide.
 6. A magnetic recording medium of a disk shape having amagnetic layer containing a magnetic material formed on a non-magneticsupport and having, between the non-magnetic layer and the magneticlayer, a layer containing a dye, of which the optical property changesby irradiation of energy rays, characterized in that, in the dyecontaining layer, continuous servo-signals based on the change of theoptical property of said dye by irradiation of energy rays are recordedon concentric tracks, wherein the dye is a polymethine-type dye which isa compound of the follow general formula (I): ##STR4## wherein, each ofR¹ to R⁴, is a hydrogen atom, a halogen atom, a hydroxyl group, acarboxyl group, an alkyl, amino, alkylamino, acryl, aryl, alkoxy,aralkyl, alkenyl or acyloxy group, X is an anion, m is 0, 1 or 2, and lis 1 or
 2. 7. The magnetic recording medium according to claim 1,wherein the magnetic layer contains a barium ferrite magnetic powder anda binder resin.
 8. The magnetic recording medium according to claim 1,wherein the servo-signals were recorded by irradiation of energy raysafter forming the layer containing a dye on the non-magnetic support,and then the magnetic layer was formed.
 9. The magnetic recording mediumaccording to claim 1, wherein the servo-signals are recorded in thelayer containing a dye, by irradiating electron beam through a patternmask corresponding to the servo-signals.
 10. The magnetic recordingmedium according to claim 1, wherein the irradiated light to record theservo-signals, is a laser having a wavelength within the maximumabsorption wavelength (λmax) range of the dye.
 11. Arecording/reproducing method for a magnetic recording medium, whichcomprises recording/reproducing magnetic data by means of a magneticrecording medium of a disk shape having a magnetic layer containing amagnetic material formed on a non-magnetic support, characterized inthat using, as said magnetic recording medium, a magnetic recordingmedium of a disk shape having a magnetic layer containing a magneticmaterial formed on a non-magnetic support and having, between thenon-magnetic layer and the magnetic layer, a layer containing a dye, ofwhich the optical property changes by irradiation of energy rays, wherein the dye containing layer, continuous servo-signals based on thechange of the optical property of said dye by irradiation of energy raysare recorded on concentric tracks, recording/reproducing of the magneticdata is conducted while tracking of a magnetic head is conducted bymeans of servo-signals detected by an optical means from the layercontaining a dye, wherein the continuous servo-signals recorded on theconcentric tracks contains signals having two signals with a differentwavelengths superposed on each other, and said two signals are uniform,respectively, and the phase difference between said two signals differssequentially from one track to the next.
 12. The recording/reproducingmethod for a magnetic recording medium according to claim 11, whereinthe layer containing a dye, is a layer having a dye compound dispersedin a binder resin.
 13. The recording/reproducing method for a magneticrecording medium according to claim 11, wherein the layer containing adye, is electrically conductive.
 14. The recording/reproducing methodfor a magnetic recording medium according to claim 13, wherein the layercontaining a dye, contains an electrically conductive substance.
 15. Therecording/reproducing method for a magnetic recording medium accordingto claim 14, wherein the electrically conductive substance is tin oxide.16. A recording/reproducing method for a magnetic recording medium,which comprises recording/reproducing magnetic data by means of amagnetic recording medium of a disk shape having a magnetic layercontaining a magnetic material formed on a non-magnetic support,characterized in that using, as said magnetic recording medium, amagnetic recording medium of a disk shape having a magnetic layercontaining a magnetic material formed on a non-magnetic support andhaving, between the non-magnetic layer and the magnetic layer, a layercontaining a dye, of which the optical property changes by irradiationof energy rays, where in the dye containing layer, continuousservo-signals based on the change of the optical property of said dye byirradiation of energy rays are recorded on concentric tracks,recording/reproducing of the magnetic data is conducted while trackingof a magnetic head is conducted by means of servo-signals detected by anoptical means from the layer containing a dye, wherein the dye is apolymethine-type dye which is a compound of the following generalformula (I): ##STR5## wherein, each of R¹ to R⁴, is a hydrogen atom, ahalogen atom, a hydroxyl group, a carboxyl group, an alkyl, amino,alkylamino, acryl, aryl, alkoxy, aralkyl, alkenyl or acyloxy group, X isan anion, m is 0, 1 or 2, and l is 1 or
 2. 17. The recording/reproducingmethod for a magnetic recording medium according to claim 11, whereinthe magnetic layer contains a barium ferrite magnetic powder and abinder resin.
 18. An information processing apparatus forrecording/reproducing magnetic data while tracking a magnetic head bymeans of servo-signals detected by an optical means from a magneticrecording medium, characterized in that a means is provided to read theservo-signals from a magnetic recording medium of a disk shape having amagnetic layer containing a magnetic material formed on a non-magneticsupport and having, between the non-magnetic support and the magneticlayer, a layer containing a dye, of which the optical property changesby irradiation of energy rays, wherein in said dye containing layer,continuous servo-signals based on the change of the optical property ofsaid dye by irradiation of energy rays, are recorded on concentrictracks, wherein the continuous servo-signals recorded on the concentrictracks contain signals having two signals with different wavelengthssuperposed on each other, and said two signals are uniform,respectively, and the phase difference between said two signals differsequentially from one track to the next.
 19. The information processingapparatus according to claim 18, wherein a means of separating theservo-signals read from the magnetic recording medium into frequencycomponents corresponding to said different two wavelengths and a meansfor outputting a positional signal from the phase difference betweensaid different two frequency components.